This invention relates generally to regulators for regulating the charging of a battery from a source of alternating current, such as an engine-driven permanent magnet alternator, and more particularly to a regulator having voltage sensing circuitry for automatically decoupling the alternating current source in response to the occurrence of an inadvertent overvoltage condition.
Engine-driven permanent magnet alternators are widely utilized as a source of battery charging current in various engine installations typically found on boats, motorcycles and other similar vehicles. Because the output voltage developed by a permanent magnet alternator is dependent on both the engine speed and the battery charge current being drawn, fluctuations in the alternator output voltage sometimes occur as the speed of the engine, and the state of charge of the battery, vary with time.
In the event the battery to be charged is electrically disconnected from the charging system, it is not unusual for a permanent magnet alternator to provide a relatively high output voltage. Such an overvoltage condition can occur not only when the battery is deliberately removed from an operating engine installation, but also when normally occurring sulphation progresses to a point where a high resistance connection is formed at the positive polarity terminal of the battery, or when vibration causes one or more of the battery cable clamps to loosen. Since it is particularly easy for these latter conditions to occur inadvertently, voltage regulators for permanent magnet alternators frequently include voltage sensing circuitry to automatically protect against circuit damage in the event of an overvoltage condition.
In some voltage regulators, such as those shown, for example, in U.S. Pat. Nos. 4,401,936 and 4,177,415, overvoltage protection is provided by shunting the output of a permanent magnet alternator in the event the alternator output voltage rises above a pre-determined threshold. In other voltage regulators, such as that shown, for example, in U.S. Pat. No. 4,220,909, conduction between the alternator and the regulator output is inhibited when the battery is disconnected from the charging system. Other examples of voltage regulators having overvoltage protection are shown in U.S. Pat. Nos. 4,405,892, 3,857,082 and 4,458,195. Attention is also directed to U.S. Pat. Nos. 4,431,959, 3,626,273 and 3,456,182.
In voltage regulators which seek to prevent excessive voltage by shunting the connection between the alternator output and the battery, it is possible for the regulator output to remain high even after the alternator output is shunted, particularly when a relatively large filter capacitor is included in the output of the battery charging system. Under certain circumstances, this can result in undesireable partial cyclical circuit operation following removal of the battery from the charging system